1. Field of the Invention
The present invention relates to a gas-filled discharge tube used, for example, as a voltage control discharge tube, a gap switching discharge tube, and a sharpener gap.
2. Description of the Prior Art
The discharge tubes are employed in various equipment, as a self-exploded (self-propelled) gap switch in voltage controllers and pulse lasers or as a sharpener gap provided immediately before a triggered spark gap switch. There is a discharge tube suited for these uses which has discharge electrodes attached at the ends of a cylinder with an inert gas sealed therein.
In such discharge tubes, when the frequency of repetitive discharge (hereinafter referred to as a discharge frequency or simply as a frequency) is high, the discharge inception voltage generally converges to a certain value as shown in FIG. 4. As the discharge frequency lowers on the other hand, the discharge inception voltage tends to increase. With this kind of discharge tubes, it is not desirable that the discharge inception voltage changes according to the discharge frequency. It is desired that the frequency vs. discharge inception voltage characteristic be flat.
As a means to improve the frequency characteristic, it has been conceived to provide a trigger wire T, which has been used in arresters, as shown in FIG. 2. This, however, has a drawback. Since the trigger wire T is formed by drawing fine wires from the both electrodes to near the middle point in the tube by using a conductive carbon paint, flashovers easily occur along the cylindrical wall of such discharge tubes as voltage control discharge tubes and spark gap switches in which high-voltage discharges are repeated for many hours. The discharge tubes are therefore easily worn and the trigger effect does not last.